Dwight Sipler wrote:

Tomatoes will get leggy if (1) they don't get enought light or (2) they
are crowded in flats before planting or (3) they are in small cells.
Planting deep works, but they get set back a few days just by getting
leggy. Best to get them started in flats, then transplant them into pots
for further growth. Space the pots apart so they have enough light
getting to the sides of the plant and they won't get so leggy (although
they do like to grow upwards). I start my tomatoes in a 288 tray,
transplant them to a 72 tray and finally to 4" pots. That seems to give
them enough soil to encourage root development. Since tomatoes are
vines, they will put down roots along the stem if they grow along the
ground. If they are in too small a cell without enough soil they will
try to push the vine out to get to another spot where there might be
better conditions.

My tomatoes get leggy in 4" and 6" pots because my light room gets too
warm in mid-May, and no amount of indoor light is enough when it's 95
degrees. I'm gonna try to get a little greenhouse set up this month so
I can get the plants outside while they are still stocky.

Best regards,
Bob